OBJECTIVES: The purpose of this study was to assess exposure to fat aerosols and aldehydes in kitchens and to study the variations in exposure between different types of kitchen. METHODS: Measurements were made in four hotel kitchens, two hamburger chain restaurants, 10 à la carte restaurants and three small local restaurants serving mostly fried food. The measurements were performed as personal measurements and each person carried two sampling devices connected to pumps. One pump was connected to a filter cassette with a 37 mm glassfibre filter and the other to a sampling device for aldehydes. The measurements were repeated on 3 days in each kitchen. Variables which could influence the level of exposure were recorded by the occupational hygienist. RESULTS: The level of fat aerosols varied between the different types of kitchen. The highest measured level of fat aerosol was 6.6 mg/m(3), in a small local restaurant. The arithmetic mean for all the kitchens was 0.62 mg/m(3). The highest level of the sum of the aldehydes was 186 micro g/m(3) (0.186 mg/m(3)), while the arithmetic mean was 69 micro g/m(3). CONCLUSIONS: The exposure to fat aerosols was modest, but could be up to 50% of the Norwegian threshold limit value (TLV) for nuisance dust (10 mg/m(3)). Fat aerosols from frying will, however, contain a mixture of heat- and water-treated fat from the meat which is being fried, hydrolysed vegetable fat and other degradation products, such as fatty acids, other organic acids and aldehydes. As a consequence of this, cooking fumes should be regarded as harmful to the lungs. The levels of formaldehyde, acetaldehyde and acrolein were well below the TLVs.